ummm lenght of the haul, type of trailer, whether the horse is used to shipping, the climate conditions, even the route can all be factors that need to be considered when hauling/shipping your horse. Lots of precautions can be taken to make it as safe as possible though. First off you want as nice a trailer as possible that is well ventaliated and has good non slip matts in it. Your horse needs to fit the trailer well, sometimes ponies are too small for slant load partions or warmbloods have very lil head room in a bumper pull. Shavings can be put in the trailer to cushion the floor and leg wraps can be applied (ask about the correct way to wrap for shipping or they can do more harm than good) to protect against bumps, bruises, and cuts in the trailer. U should haul in the most temperate part of the day, avoid the heat and possible traffic by shipping at night or in the winter all in the heat of the day to avoid extreme cold and ice. Stop every three to four hours and offer your horse water and check that wraps, ties and the trailer is secure and traveling correctly. Never haul more than about six hours without off loading and walking your horse for at least an hour or so. Preferably stopping for the night with a paddock to turn out in. Oh and giving your horse a hay bag or net might distract him and make the ride more comfomy, mine munch a while and then sleep on their hay nets like pillows. If you use a hay net it's best to use a fly mask to protect your horse's eyes from flying debris and if ur horse isn't a good shipper or doesn't like the trailer, leg wraps, a head bumper, and a fly mask are a must.
I've heard the analogly that shipping one mile takes the same amount out of the horse that walking it would. So keep that in mind. Also if ur getting tired of driving or being in the car it's prolly time to rest and let your horse have a break as well. There are several sites on google that offer over night safe stabling at campsites and hotels all over the nation so you can plan your trip effectively.
Competing and shipping horses all over the South East US